Gio benitez tonight. Thanks to you. A man wielding knives held police at bay all while tourists watched. Reporter: Chaos erupted as crowds were watching the famous changing of the guard at buckingham palace. A man burst forward brandishing knives holding one to his neck. When he refused to put the weapons down, police moved in taking him down with a taser. Bystanders were stunned by how quickly it unfolded. They tased him and he fell to the ground in a couple of seconds. Reporter: Tourists captured the drama on their cameras and phones, posting the videos on youtube. Police say the man is believed TO BE IN HIS 50s. So far they haven't released any other information about him or his motive. We're told the queen wasn't home at the time. In the end, nobody was seriously injured.

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